1. Field of the Invention
The present invention is in a novel soluble pentacene precursor, an intermediate for the precursor, a method for the preparation of the precursor and products resulting from use of the new precursor.
2. Description of the Related Art
It is widely recognized that pentacene (C22H14) is a preferred organic semiconducting material for the fabrication of organic thin film transistors (OTFT) due to its high electron mobility, improved on-off ratio, improved environmental stability and better reliability than most other organic semiconductors. Pentacene is recognized as a viable alternative to inorganic thin films based on Si or Ge for transistor applications. A major drawback to using pentacene is that the compound has a low solubility in most solvents. The lack of a suitable solvent not only makes the purification of pentacene difficult but also necessitates the use of difficult procedures, such as vapor phase deposition under high vacuum, in order to cast a film on a TFT device.
Considerable effort has been devoted in an attempt to prepare “soluble” pentacene precursors in order to overcome this problem. The availability of a soluble material would facilitate the preparation of solid films through one or more of the known operations of spin-coating, spray coating, screen printing or inkjet printing. Of course, the precursor must be soluble in solvents which are commercially permissible.
Several pentacene precursors have been reported. Most of the reported precursors are cyclic adducts of pentacene and another minor fragment. One such cyclic adduct is shown in U.S. Pat. No. 6,963,080. The adduct is produced by way of a Diels-Alder reaction using, inter alia, N-sulfinyamides as the dienophile. But such compounds can be difficult to work with.
Solid films of large size can be prepared by spin-coating the precursor solutions. After the films are dried, a chemical reaction is triggered either by heat or by light to expel the volatile minor fragment. Subsequently, the resulting films of pure pentacene are annealed at a proper temperature for self-reorganizing of their morphology, which is crucial for promoting their charge mobility.